Conventionally, imaging apparatuses for irradiating an object with radiation, detecting the intensity distribution of radiation having passed through the object, and obtaining a radiation image data of the object have generally been used for industrial nondestructive inspections and medical diagnoses. As a typical imaging method of such imaging apparatuses, the film-screen method is available. In this method, radiation imaging is performed with a combination of a photosensitive film and a phosphor having a sensitivity to radiation. To be specific, a sheet of a rare-earth phosphor, which emits light in response to irradiation, is bonded and held on both sides of a photosensitive film, radiation having passed through a subject is transformed into visible light through the phosphor, and the light is captured by the photosensitive film. A latent image formed on the film can be visualized by development through a chemical treatment.
As digital technology has improved in recent years, the following method has become widely available: a radiation image is converted into an electric signal, the electric signal is subjected to image processing, and then the signal is reproduced on a CRT or the like as a visible image, so that a radiation image with high image quality can be obtained. For example, a radiation image recording/reproducing system is proposed in which a transmission image of radiation is temporarily stored in a phosphor as a latent image, and then the latent image is photoelectrically read by irradiation of excitation light such as laser light, so that a visible image is obtained.
Further, as semiconductor process technologies have improved in recent years, apparatuses for photographing radiation images using semiconductor sensors have been developed. These systems have a considerably wide dynamic range as compared with conventional radiation photographing systems using photosensitive films, and have a practical advantage of obtaining a radiation image not affected by fluctuations of the exposure amount of radiation. Further, unlike the conventional photosensitive film system, an output image can be obtained instantly without the need for a chemical treatment.
FIG. 9 is a conceptual diagram showing a system using such a radiation imaging apparatus 103. Radiation from a radiation generating device 101 is emitted to a subject 102, and radiation having passed through the subject reaches a radiation sensor 104 included in the radiation imaging apparatus 103. In the radiation sensor 104, radiation is transformed into visible light through a phosphor and detected as an electric signal by an photoelectronic converter arranged in a two-dimensional lattice. A control unit 105 is provided for controlling driving for reading, image transfer, and so on of the radiation sensor 104. The control unit 105 performs digital image processing on an image signal outputted from the radiation sensor 104, and displays the signal as a radiation image of the subject 102 on a monitor 106. The advantage of the system shown in FIG. 9 is that an image can be instantly monitored unlike the above radiation image reading/reproducing system which reads an image in post-processing. In such an imaging system, the radiation sensor 104 is set on a dedicated stand according to an imaging pattern such as a standing position or a lying position, and is properly set as necessary.
Conventionally, this kind of imaging apparatus has been placed and used in a radiation room. In recent years, however, a transportable imaging apparatus (called electronic cassette) has been developed with a small thickness and a light weight in order to attain faster and wide-range imaging. Thus, there is proposed an imaging system applicable to a round of visits as well as cassette imaging in a radiation room (see Japanese Patent Laid-Open No. 11-99144). Such an imaging system is quite useful because it is possible to solve the following problems: a number of cassettes have to be carried for storing conventional films and fluorescent screens during a round of visits, and imaging has to be performed again in the event of an imaging error which cannot be instantly confirmed.
The movable radiation imaging apparatus above requires, as a minimum, a battery which supplies electric power for generating radiation. Besides, in recent years, some imaging apparatuses include batteries capable of supplying electric power used for power for movement. When the electronic imaging apparatus above (e.g., electronic cassette) is used, more electric power is required and the capacity of the battery must be increased in order to drive the imaging apparatus. When a larger capacity battery is used, the weight and outer dimensions of the battery increase, adversely affecting the outer shape of the apparatus. Thus, such a large battery is unacceptable in view of operationality. However, when a small capacity battery is used, it must be charged very frequently, and the rate of operation may decrease.
When the mobile radiation imaging apparatus is moved, an operation unit may be carelessly touched and the apparatus may perform an unnecessary operation. Such an unnecessary operation wastes power. If persons to be imaged can be displayed on a list when the apparatus is moved, an examiner can conveniently confirm, for example, the next person to be imaged. However, when the overall apparatus is turned off while being moved, a list of persons to be imaged cannot be displayed on a display, thereby considerably degrading operationality. Therefore, in the case where the radiation imaging apparatus is moved while power is turned on, power conservation measures are desired for preventing an unnecessary operation caused by an operating error or the like and also reducing power consumption.